The invention is directed to a change spur gear for vehicles in layshaft design with a starting member, a main shaft train and two layshafts, and which can be shifted under power.
Automotive transmissions of that type employ primarily synchronizing devices for shifting such as previously known, e.g., from the German Offenlegungsschrift No. 32 17 950 and consisting of a sliding sleeve which prior to engaging the mating component forces a synchronization of the two components to be coupled, through a friction cone clutch. For that purpose, however, the flow of force from the engine is interrupted, the shifting occurs essentially at no power, and only the participating rotating transmission masses need to be accelerated or retarded accordingly by means of the synchronizing device.
The invention is based on a transmission previously known from the German Patentschrift No. 958 081 which as a starting member features a friction clutch followed by a spur gearing which is comprised of the main shaft and a layshaft. In addition a synchronizing device is arranged on a second layshaft, which is also called an auxiliary shaft. The operational flow of force proceeds through the gear wheels and the shift detents, which are on the main shaft and one of the layshafts, are in mesh in the various gears. Arranged on the second layshaft are further gear wheels and shift detents which are effective only during the gear shift phase. For that purpose, a gear change is prepared by forcing sliding sleeves equipped with deflecting detents axially onto respective mating detents. The gear change itself takes place through friction clutch release whereby a rotational speed adaptation of the detents to be shifted, to the next gear, occurs on the second layshaft through the synchronizing device. While the engagement of the detents occurs in the absence of power, it takes place under axial pressure as long as an inequality of speed exists and the end faces of the detents run on one another in ratchet fashion.
A similar transmission is previously known from the German Patentschrift No. 697 552. The flow of force occurs there also by way of gear wheels on the main shaft, the layshaft and through sliding shift sleeves. A friction synchronizing clutch is capable of effecting engagement synchronization of the shifting sleeves by connecting the main shaft with the transmission output shaft or by braking on a casing-fixed braking surface. The engagement itself occurs again at no power and with the friction main clutch released. Also known is a transmission design (German Pat. Nos. 739,638 and 881,003) where the friction main clutch is bridged by a shiftable clutch which is supposed to effect synchronization directly through the layshaft of the transmission. The transmission designs mentioned above do not represent a power shift gear with uninterrupted gear shifting.
Another design of a change spur gear in layshaft design is shown by German Auslegeschrift No. 1 076 461. It teaches as a starting element a torque converter which is followed by two or more gears stages which are shifted and/or synchronized by multiple disk and/or friction clutches.
The synchronizing device designs described above have the drawback that there are always friction bodies, that is, multiple disks, friction cones or ratchet type detents, that participate in the shifting operations. These detents are subject to heat buildup, wear and increased risk of breakage with the result of susceptibility to malfunction and repair, reduced service life and short lubricating oil life, especially when the main clutch is designed as a friction clutch.
These disadvantages are partly counteracted by a transmission design known from the German Pat. No. 1 246 010 where a mechanical multi-step reduction gear is driven by two torque converters and the synchronization takes place either through filling and emptying of the converters or through an integrated hydrodynamic brake. But the deflection detents are always in a ratchet mode as long as the synchronization process is not completed. While they operate satisfactorily, the hydromechanical transmission of the above design or other non-wearing fully hydraulic transmissions are afflicted with the disadvantage that the force of flow occurs in all gear stages through a hydrodynamic circuit, i.e., through a torque converter or a fluid clutch. The efficiency of the transmission is considerably lower than with strictly mechanical automotive transmissions, especially outside the starting range.
The problem to which the invention is directed is to provide a shift gear which is shiftable under power and without traction force interruption, which transmission combines great reliability, absence of wear of the components participating in the shifting operations, good efficiency, and low design expense. Further, the transmission should be capable of being equipped with various numbers of gears and to permit automatic shifting.